This needs to cater for different scenarios.

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* Typical monthly subscriptions - a fixed fee linked to a standard product or service per month, like SaaS or hosting etc.

* Customer specific recurring charges (ie: annual or monthy) like support fees etc. The fee would need to be updateable via the admin to cater for changes over time.
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Ideally, options would include automatic charge via credit card (don't know how this works without retaing details although the big players seem to be able to do so) OR automatically sending a pdf invoice to the billing email address. I'd also expect that the current status (eg: paid up or not) could be manually updateable against the customer record so that it could automatically control access to Customers / Partners only content on the site (refer other thread).

Not asking for much am I :-)

Cheers

JP